1. Field of the Invention
The present invention relates to a stabilized syrup with the highest possible amount of trehalose, more particularly, to a non- or substantially non-crystalline high trehalose content syrup which dissolves trehalose in an amount over the water solubility and dissolves other oligosaccharide having a trehalose structure within the molecule, and uses thereof, as well as to a method for preventing the crystallization of trehalose in high trehalose content syrups, an agent for preventing the crystallization of trehalose syrups which contains as an effective ingredient at least one oligosaccharide having a trehalose structure within the molecule, and a process for producing the syrups.
2. Description of the Prior Art
Trehalose or .alpha., .alpha.-trehalose has long been known as a non-reducing saccharide consisting of glucose molecules. As described in "Advances in Carbohydrate Chemistry", Vol.18, pp.201-225 (1963), published by Academic Press, USA, and "Applied and Environmental Microbiology", Vol 56, pp.3,213-3,215 (1990), trehalose widely exists in microorganisms, mushrooms, insects, etc., though the content is relatively low. Since non-reducing saccharides including trehalose do not react with amino group-containing substances such as amino acids and proteins, they neither induce the amino-carbonyl reaction nor affect the substances. Thus, non-reducing saccharides have been believed to be used without fear of causing unsatisfactory browning and deterioration. Because of these, it has been in great demand to establish preparations of such non-reducing saccharides.
In conventional preparations of trehalose, as disclosed in Japanese Patent Kokai No.154,485/75, microorganisms are used or as proposed in Japanese Patent Kokai No.216,695/83, maltose is converted into trehalose by using maltose- and trehalose-phosphorylases in combination. The former, however, is not suitably used on industrial-scale preparations because the content of trehalose present in the microorganisms as starting material is usually less than 15 w/w % (the wording "w/w %" will be abbreviated as "%" in the specification, if not specified otherwise), on a dry solid basis (d.s.b.) and the extraction and purification steps used are complicated. The latter has the following demerits: Since trehalose is formed via glucose-1-phosphate, (i) maltose as a substrate could not be used at a relatively-high concentration; (ii) the enzymatic reaction systems of the phosphorylases are reversible reactions, and the yield of the desired trehalose is relatively low; and (iii) it is substantially difficult to keep their reaction systems stably and to continue their enzymatic reactions smoothly. Thus, no such a method has been realized as an industrial-scale preparation.
As regards the preparation of trehalose, it is reported in the column titled "Oligosaccharides" in the chapter titled "Current Status of Starch Application Development and Related Problems" in "Food Chemicals", No.88, pp.67-72 (August, 1992) that "In spite of a wide applicability of trehalose, an enzymatic preparation thereof via a direct saccharide-transfer reaction or a hydrolytic reaction has been reported to be scientifically almost impossible in this field." Thus, an enzymatic preparation of trehalose from material starches has been believed to be scientifically very difficult.
It is known that partial starch hydrolysates prepared from starches as materials such as liquefied starches, cyclodextrins, and maltooligosaccharides usually contain reducing end-groups as end units. These partial starch hydrolysates are referred to as "reducing partial starch hydrolysates" in the specification. The reducing power of such reducing partial starch hydrolysates is generally expressed by "Dextrose Equivalent (DE) value", based on their dry solid. It is known that among reducing partial starch hydrolysates those with a relatively-high DE generally have a lower molecular weight and viscosity, as well as a relatively-high level of sweetness and reactivity, and easily react with substances having amino groups such as amino acids and proteins to cause unsatisfiable browning, smell, and deterioration of their quality.
These properties of reducing partial starch hydrolysates are varied depending on their DE values, and the relationship between reducing partial starch hydrolysates and their DE values is very important. It has been even believed to be impossible to break off the relationship in this field.
The only way to break off the relationship is to form non-reducing saccharides from reducing partial starch hydrolysates by hydrogenating the hydrolysates at a relatively-high hydrogen pressure to convert their reducing end-groups into hydroxyl groups. The method, however, requires a considerably-high-pressure autoclave, consumes excessive amounts of hydrogen and energy, and also requires a relatively-high level of control or safety facility to prevent disasters. The material reducing partial starch hydrolysates and the resultant products differ because the former consists of glucose units and the latter, i.e., sugar alcohols of the resultant partial starch hydrolysates, consists of glucose and sorbitol units which may cause symptoms such as digestive disorder and diarrhea when administered to the body. Thus, it has been in great demand to establish a method to decrease or even eliminate the reducing power of reducing partial starch hydrolysates without changing the chemical structure of glucose as a constituent saccharide thereof.
To overcome these problems, the present applicant, as disclosed in Japanese Patent Kokai No.143,876/95, disclosed a novel non-reducing saccharide-forming enzyme which forms non-reducing saccharides having a trehalose structure as an end unit from one or more reducing partial starch hydrolysates with a glucose polymerization degree of at least 3, and established a method for producing non-reducing saccharides with a trehalose structure as an end unit and a glucose polymerization degree of at least 3 and a method for producing trehalose from the non-reducing saccharides.
As disclosed in Japanese Patent Kokai No.213,283/95, the present applicant disclosed a novel trehalose-releasing enzyme which specifically hydrolyzes the bonding between a trehalose moiety and other moiety in non-reducing saccharides with a trehalose structure as an end unit and a glucose polymerization degree of at least 3 (the enzyme is designated as "trehalose-releasing enzyme" in the specification, hereinafter) and a method for producing trehalose in a relatively-high yield by using the above non-reducing saccharide-forming enzyme and the trehalose-releasing enzyme. The applicant also disclosed in Japanese Patent Kokai No.170,977/95 a maltose/trehalose converting enzyme which directly converts maltose into trehalose from reducing partial starch hydrolysates.
Thereafter, during the study of the uses of trehalose, the present applicant found that besides powdery crystalline products such as hydrous- and anhydrous-crystalline trehalose, much more required is a high trehalose content syrup which can be tank-stored, pump-transported, transported by tank trucks, and easily handled. However, it was found that trehalose has a relatively-low water solubility and an unsaturated trehalose solution has a relatively-low concentration, and this easily allow bacteria to grow and results in bacterial contamination, while a saturated trehalose solution is highly-unstable at ambient temperature and this easily causes trehalose to crystallize into crystalline trehalose hydrate and to easily lose its homogeneous fluidity as a feature of trehalose syrups, resulting in serious affects on tank-storage and pump-transportation. In view of these, stable trehalose syrups with the highest possible amount of trehalose have been required.
To solve the aforesaid drawbacks, the present applicant studied and found that, as disclosed in Japanese Patent Application Nos.110,291/95 and 112,159/96, syrups which dissolve trehalose over the water solubility and dissolve other saccharides, preferably, those which dissolve trehalose over the water solubility and other saccharides in an amount of not lower than the amount of trehalose, more preferably, those which dissolve 18.5-25.0% trehalose and other saccharides in an amount of not lower than the amount of trehalose and contain 25-35 w/w % moisture are stable at ambient temperature and agreeable to the object of the present invention. After further studying, it was found that the above high trehalose content syrups, however, are defective in their insufficient trehalose content and a relatively-high DE as a whole. Therefore, highly required are high trehalose content syrups which have a lower DE and a satisfactory stability at ambient temperature